Many modern communications systems use reference signals, such as channel state information reference signals (CSI-RS), transmitted by an access node to assist User Equipment (UE) in measuring communications channels between the access node and the UE. As an illustrative example, the access node transmits a CSI-RS and a UE uses the CSI-RS to measure the communications channel and generate channel information, such as a channel quality indicator (CQI), precoding matrix index (PMI), rank indicator (RI), and the like, which it feedbacks to the access node. Access nodes may also be commonly referred to as evolved NodeBs (eNBs), base stations, NodeBs, master eNBs (MeNBs), secondary eNBs (SeNBs), remote radio heads, access points, and the like, while UEs may also be commonly referred to as mobiles, mobile stations, terminals, subscribers, users, stations, and the like. A transmission point (TP) may be used to refer to any device capable of transmitting. Therefore, transmission points may refer to access nodes, eNBs, base stations, NodeBs, MeNBs, SeNBs, remote radio heads, access points, UEs, mobiles, mobile stations, terminals, subscribers, users, and the like. A transmit-receive point (TRP) refers to a TP that also is capable of receiving.
Generally for massive Multiple Input Multiple Output (massive MIMO) or 3D MIMO communications systems, there are large numbers of transmit antennas (or ports) at the eNB. Therefore, the eNB would have to transmit a large number of CSI-RS signals in order to facilitate channel information between each transmit antenna (or ports) and each receiver antenna at each UEs. The transmission of the large number of CSI-RS would significantly impact overall communications system performance by consuming a large amount of beamformed resources as overhead.